Environmental changes such as global warming can affect ecological communities by altering individual life histories and species interactions. Recent studies focusing on the consequences of environmental change on species interactions highlighted the need for a wider, multi‐species context including both trophic and non‐trophic interactions (e.g. predator interference). However, the effects of biotic and abiotic factors on trophic and non‐trophic interactions remain largely unexplored. To fill this gap, we combined laboratory experiments and functional response modelling to investigate how temperature and prey density influence trophic and non‐trophic interactions in multiple predator communities. The system under study consisted of predatory dragonfly larvae (Aeshna cyanea) and omnivorous marbled crayfish (Procambarus virginalis) preying on common carp fry (Cyprinus carpio). We estimated the functional response of each predator in single‐predator experiments and used this information to disentangle the trophic and non‐trophic interactions and their dependence on environmental conditions in multiple predator trials. We found that consumer identity, prey density, and temperature all affect the magnitude of trophic and non‐trophic interactions. Non‐trophic interactions mostly decreased predator feeding rates, corroborating previous observations that interference prevails in aquatic communities. Moreover, trophic interactions depended primarily on the environmental variables whereas non‐trophic interactions depended mainly on consumer identity. Our results indicate that non‐trophic interactions among true predators and omnivores can be substantial and that biotic and abiotic conditions further modify the magnitude and direction of these interactions, which can affect food web dynamics and stability.

Female crayfish stores male gametes after mating until the beginning of egg laying and fertilization. The aim of the present study was to investigate the duration of post-mating spermatophore storage as well as the timing and temperature of spawning in two crayfish species of economic importance, namely the signal crayfish Pacifastacus leniusculus and the noble crayfish Astacus astacus. Results showed that the average duration of the post-mating spermatophore storage is significantly (P<0.05) longer in the noble crayfish (34.6±1.7 days, range: 19 to 60 days) than the signal crayfish (3.9±0.5 days, range: 1 to 18 days). The highest percentages of the post-mating spermatophore storage duration in the signal crayfish (46.5%) and the noble crayfish (44.5%) were 1 and 31 to 40 days, respectively. While there is an overlap in the timings of mating and egg laying in the signal crayfish, these two reproductive processes were not observed at the same days in the noble crayfish and there was at least 2 weeks interval between last mating and first egg laying individuals. Average mating and egg laying temperatures were significantly (P<0.05) higher in the signal crayfish than the noble crayfish. The average temperatures for mating in both species were significantly (P<0.05) higher than the temperatures that they utilized for egg laying. In conclusion, female noble crayfish stores post-mating spermatophores a longer duration compared with the signal crayfish. Also, the signal crayfish mates and lays egg in temperatures that are higher than the noble crayfish. Spawning season is shorter in the signal crayfish compared with the noble crayfish. The results of present study provide information contributing to the crayfish broodstock management in aquaculture.

The ultrastructure of spermatozoa in three species of cambarid crayfish, Cambarus robustus, Orconectes propinquus, and Orconectes rusticus, were studied and compared with eight previously studied species from different crayfish families using morphological features and biometrical data. The ultrastructure of spermatozoa show a generally conserved pattern including an acrosome and nucleus in the anterior and posterior parts of the cell, respectively, radial arms that wrap around the nucleus, and the whole cell is enclosed by an extracellular capsule. The most outstanding morphological feature in spermatozoa of three studied cambarid crayfish is the crest-like protrusions in the anterior part of the acrosome that can be used as one of the features for distinguishing the members of this family. Results of biometrical data reveal that acrosome size in the representatives of Parastacidae are the smallest, while representatives of Astacidae show the biggest acrosome. The acrosome size in species belonging to Cambaridae occupy an intermediate position between the two other families of freshwater crayfish. In conclusion, a combination of morphological features and biometrical data of spermatozoa can help distinguishing different species of the freshwater crayfish.